virtual PC 2007 write-protected a drive and it is stuck in read-only mode!

I installed Virtual PC 2007 on Vista Ultimate 64.
The virtual machine is Windows XP.
When I decided to share one of the host drives (a USB2 attached 500GB drive), it does not allow files to be saved or changed on the drive from either the host machine or the virtual machine.
Even when the virtual machine is shutdown, access is only read-only. There are no NTFS permissions set, so I am completely stumped as how to get the drive back to normal read-write mode (as it was before installing VPC 2007)

The drive share was mounted in nowhereland by some unknown process (VPC was completely off and all processes killed)
run the following from the command line (as admin)
- what I can't figure out is why shared drives in Virtual PC 2007 are always read-only (even though they are not set that way)

What do you mean you shared one of the host drives? do you mean that you unmounted it from the host and created a linked drive?
VPC doesn't really do what you're saying, unless I'm mis-reading what you're doing. When you say shared drive are you referring to VPC's Linked disks?

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I just looked at it again, I did mean shared drive, only shared from within the Virtual Machine Settings (not a typical share, like a network share). There is a setting called "Shared Folders" within the VM Settings that you can pick 1 or more shared folders. I presume that's what a "linked" drive is?

If you go directly to the host's drive and look at it's properties, there are no shares defined (Even if the folder is shared within the VM).
I had a portable drive with a letter E:\ shared within the VM (but not anywhere else) when the drive decided to become "read-only". Though, it could be coincidental that this happed with VPC and completely unrelated.

Got it. Shared Folders shoudl work, but my guess here might be Vista permissions. Are you running VPC as admin?
Also, depending on what you're doing, large file copies, folders with very large numbers of files, Shared Folders isn't the best solution. Standard Windows network shares will work better.
VPC's shared folders aren't designed as a replacement for network sharing, but more like a supplement.

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